The present invention generally relates to an image processing apparatus, and more particularly to an image processing apparatus for smoothing an outline of an image to be processed and outputting a set of correction dots to an output device, so as to produce a visually smooth outline of the image in the output device.
When an image data including graphics and character information is processed and output to an output device, the image data supplied to the output device is usually made up of a matrix of dots arranged in a regular-manner horizontally and vertically. FIG. 1A is an enlarged view showing an example of the output image data including horizontal and vertical rows of dots. An edge portion of an output image, which is inclined with respect to a horizontal or vertical direction, often shows stair-like irregularity that would be appreciable to the human eyes when the image is reduced back to the original size. Such stair-like irregularity is hereinafter called an aliasing. A conceivable method for eliminating such stair-like irregularity from the edge portion of the image (this method is hereinafter called anti-aliasing) is to add suitable gradation dots to each related dot of the edge portion of the image as shown in FIG. 1B so that the output image would show a visually smooth outline with no irregularity. Such a conventional image processing apparatus is disclosed, for example, in Japanese Laid-Open Patent Application No. 57-24268. However, there is a problem in that the conventional image processing apparatus in which gradation dots or halftone dots suitable for being added to the output image requires the use of a complicated control unit for processing such an image data including the gradation dots by executing complicated calculations for an outline smoothing process. And, the conventional apparatus must be provided with an image data memory having a relatively large capacity for storing additional gradation data as well as the image data, and an output device to which the image data is supplied from the conventional image processing apparatus must have a complicated output control and function for outputting the tone dots supplementary to the image data including stair-like irregularity or aliasing.